This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for Light Converting Apparatus of Projection System earlier filed in the Korean Industrial Property Office on Apr. 24, 2001 and there duly assigned Serial No. 2001-22100.
1. Field of the Invention
The present invention relates to a projection display device, and more particularly, to a projection display device having a high optical efficiency.
2. Description of Related Art
A liquid crystal (LC) projector includes an LC panel as a modulator for modulating light from a light source to form an image. The LC panel is divided into two types including a transmissive type and a reflective type. A poly-silicon liquid crystal display is mainly used as the transmissive LC panel, and a digital micromirror device (DMD) and a liquid crystal on silicon (LCOS) device are mainly used as the reflective LC panel.
Of these, the LCOS display recently receives an attention due to a small size and a high resolution. In the LCOS display, a three-panel LC projector or a single-panel LC projector has been used to achieve a full color.
A conventional LCOS projection display device includes a light source, a fly-eyes lens, a polarization converting unit, a condensing lens, a color separating unit, a polarizing beam splitter, a reflective liquid crystal panel, and a projecting unit.
The fly-eyes lens makes light emitted from the light source uniform. The polarization converting unit converts the uniformized light into a p-wave polarized light. The condensing lens condenses the p-wave polarized light. The color separating unit separates red (R), green (G) and blue (B) light rays from the p-wave polarized light. The liquid crystal panel generates s-wave polarized lights and p-wave polarized lights by a switching operation according to the image signals. The polarizing beam splitter reflects the s-wave polarized lights and transmits the p-wave polarized lights. The projecting unit enlarges and projects the s-wave polarized lights to form a color image on a screen.
The polarization converting unit includes a plurality of prisms which allow a p-wave light to be transmitted and reflect a s-wave light. Light shielding films are disposed on the front surfaces of the prisms at prism-height intervals, and retardation films (i.e., half-wavelength plate) are disposed on the rear surface of the prisms opposite to the light shielding films to convert the s-wave light into the p-wave light. Here, an unpolarized light is converted into a polarized light while passing through the prism.
The projection display device having such a configuration achieves a sufficient amount of light. However, in order to make the light enter, only a half of the polarization converting unit, a refraction of the fly-eyes lens and a distance between two fly-eyes lenses must be adjusted. This results in increasing an angle distribution of light by twice due to Lagrange invariant. In this case, there occurs a problem in that a large size of optical components is required, and a contrast ratio is lowered.
In addition, in case of reducing an angle distribution of light, a brightness of the projection display device deteriorates significantly.
In the efforts to overcome the problem described above, a polarizing beam splitter is employed.
U.S. Pat. No. 5,446,510 issued to Mitsutake et al. for Image Display Apparatus, discloses an image display apparatus having a polarizing beam splitter. A xc2xc-wavelength plate and a mirror are disposed over the polarizing beam splitter, and a total reflection prism is employed on an optical axis therein. However, in the image display apparatus having such a configuration, light converted into a p-wave light is irradiated while forming two peaks, thereby deteriorating a uniformity of irradiated light.
It is therefore an object of the present invention to provide a projection display device having excellent optical efficiency.
It is another object of the present invention to provide a projection display device having a high brightness.
It is still another object of the present invention to provide a projection display device having a high light uniformity.
In order to achieve the above and other objects, the preferred embodiments of the present invention provides a projection display device including a light source supplying light having an s-wave light and a p-wave light; a first polarizing beam splitter including a reflecting surface, transmitting the p-wave light and reflecting the s-wave light; a retardation film arranged between the light source and the polarizing beam splitter to cover a portion of a front surface of the polarizing beam splitter, and converting the s-wave light into the p-wave light and the p-wave light into the s-wave light; a mirror re-reflecting the s-wave light reflected from the reflecting surface of the first polarizing beam splitter toward the reflecting surface of the first polarizing beam splitter, so that the s-wave light directs toward the retardation film.
The projection display device further includes a fly-eyes lens making the p-wave light passing through the first beam splitter uniform; a condensing lens condenses the light passing through the fly-eyes lens; a color separating unit separating R, G and B lights from the light passing through the condensing lens; a modulating unit modulating the R, G and B lights incident thereto to output a p-wave light and a s-wave light; a second polarizing beam splitter transmitting the p-wave light and reflecting the s-wave light; and a projection unit enlarging and projecting the s-wave light to form a color image on a screen.
The light source includes a lamp and a parabolic reflector, and light emitted from the lamp is reflected by the parabolic reflector, so that parallel light directs toward the retardation film. An angle of an optical axis is 45xc2x0. The retardation film is a half-wave plate or a quarter wave plate. The retardation film covers a half of the front surface of the first polarizing beam splitter. The retardation film has a triangular cross-section or a rectangular cross section. The modulating unit is a reflective liquid crystal display (LCD).